681  Convex Hull Finding
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 New poster
 Posts: 8
 Joined: Thu Dec 04, 2003 4:56 pm

 New poster
 Posts: 8
 Joined: Thu Dec 04, 2003 4:56 pm

 New poster
 Posts: 8
 Joined: Thu Dec 04, 2003 4:56 pm
Mind one thing... in 681 problem given input is naturaly sorted so we needn't to do that again. I think your sample is incorrect according to program input.wyvmak wrote: when i implemented Graham scan, i used the following points to check my Graham scan:
1
15 // number of points
0 0
0 1
0 2
0 3
0 4
1 3
2 2
3 3
4 4
4 3
4 1
4 0
3 0
2 0
1 0
i hope that can help.
I am afraid that the test case itself is not correct.miko'mized wrote:hm maybe that's wrong ... for this test:
1
7
0 6
4 4
6 2
2 2
0 4
1 4
4 4
anwser is:
1
7
0 4
1 4
4 4
0 6
4 4
6 2
0 4
right?
However, in your test case, the first and the last vertex aren't the same. Anyway, I am still getting WA with Graham Scan.Since all the shapes are closed contours, therefore, the last vertex should be identical to the first vertex.
681
I've got TLE,RE and WA 10+ times,but haven't got AC!
Can anyone give me some hint or test data so I can find what is wrong
int my program? Thank you!
I try to extend the array to store the points but still got wa!
What is the special judge data of this problem?
WA after repeated tries
Code: Select all
[cpp]
#include <iostream>
#include <vector>
#include <stack>
using namespace std;
struct point
{
int x, y;
point (int a=0, int b=0):x(a),y(b){}
int operator*(const point &b)
{
return x*b.yy*b.x;
}
point operator(const point &b)
{
return point(xb.x,yb.y);
}
};
int main()
{
int k, n;
cin>>k;
cout<<k<<endl;
while(k)
{
vector<point> t;
point s;
cin>>n;
for(int i=1; i<n; i++)
{
cin>>s.x>>s.y;
t.push_back(point(s.x,s.y));
}
int wa;
cin>>wa>>wa>>wa;
int m=0;
point mi=t[0];
for(int i=1; i<t.size(); i++)
{
if(t[i].y<mi.y)
{
mi.x=t[i].x;
mi.y=t[i].y;
m=i;
}
else if(t[i].y==mi.y)
{
if(t[i].x<mi.x)
{
mi.x=t[i].x;
m=i;
}
}
}
vector<point> z;
for(int i=m; i<t.size(); i++)
z.push_back(t[i]);
for(int i=0; i<m; i++)
z.push_back(t[i]);
t=z;
t.push_back(t[0]);
stack<point> r;
r.push(t[0]);
r.push(t[1]);
for(int i=2; i<t.size();)
{
if(r.size()==1)
{
r.push(t[i]);
i++;
continue;
}
point p=r.top(); r.pop();
point next=r.top(); r.push(p);
int val=((nextp)*(pt[i]));
if(val>=0) // changed it to val>0 (still WA)
{
r.push(t[i]);
i++;
}
else
{
r.pop();
}
}
vector<point> ans(r.size());
while(!r.empty())
{
ans[r.size()1]=r.top();
r.pop();
}
cout<<ans.size()<<endl;
for(int i=0; i<ans.size(); i++)
cout<<ans[i].x<<" "<<ans[i].y<<endl;
if(k)
cout<<1<<endl;
}
return 0;
}
[/cpp]
thx
abi
I used Grahm's scan and got WA. With almost identical code I passed convex hull problem on USACO. I've checked test cases posted above, works fine. Anyone has an idea about where the error might be? Any new test data?
Code: Select all
// FINDING THE COMPLEX HULL USING GRAHM'S SCAN
#include <cstdio>
#include <vector>
#include <algorithm>
#include <utility>
#include <iterator>
#include <cstdlib>
#include <cmath>
#define EPS 0.0000001
#define PI pair < int ,int >
using namespace std;
PI F;
double dist(PI A,PI B) { // Returns squared distance
return 1.0*(A.firstB.first)*(A.firstB.first)+(A.secondB.second)*(A.secondB.second);
}
double sta(PI A,PI B,PI C) {
return 0.5*(A.first*B.secondA.second*B.first + A.second*C.first  A.first*C.second + B.first*C.second  C.first*B.second ) ;
}
class compare_angle {
public:
bool operator() (PI A,PI B) {
if (fabs(sta(F,A,B))<EPS)
if (dist(F,A)<dist(F,B)) return 1; else return 0;
else
if (sta(F,A,B)>EPS) return 1; else return 0;
}
};
class pair_compare {
public:
bool operator() (PI A,PI B) {
if (A.second==B.second) return A.first<B.first;
else return A.second<B.second;
}
};
void output(vector <PI> & Q) {
Q.push_back(Q.front());
printf ("%d\n",Q.size());
for (int i=0;i<Q.size();i++)
printf ("%d %d\n",Q[i].first,Q[i].second);
}
int main() {
int test_cases,temp;
scanf ("%d",&test_cases);
printf ("%d\n",test_cases);
for (int t=0;t<test_cases;t++) {
vector < PI > V;
vector < PI > hull;
int N;
if (t!=0) scanf ("%d",&temp);
scanf ("%d",&N);
V.resize(N);
hull.resize(N);
for (int i=0;i<N;i++)
scanf ("%d %d",&V[i].first,&V[i].second);
// Sort and remove duplicates
sort(V.begin(),V.end(),pair_compare());
V.resize(distance(V.begin(),unique(V.begin(),V.end())));
N=V.size();
if (N<=4) {
output(V);
} else {
// Sort according to angle
F=V[0];
vector < PI >::iterator VIT=V.begin();
VIT++;
sort(VIT,V.end(),compare_angle());
V.push_back(F);
hull[0]=V[0];
hull[1]=V[1];
int top=1,i=2;
while (i<=N)
if (sta(hull[top1],hull[top],V[i])<EPS)
top;
else {
top++;
hull[top]=V[i];
i++;
}
hull.resize(top);
output(hull);
if (t!=test_cases1) printf ("1\n");
}
}
return 0;
}
I'm olso getting WA for this problem and I'm going crazy because my program answers right to all of my tests and tests which I find in this page.I use Graham's Algorithm for finding Convex Hull and also solve (with the same programm(with some little changes)) problem 10065.
Please somebody give me some good tests.
Thanks.
Please somebody give me some good tests.
Thanks.
someone who like to solve informatic problems.
http://acm.uva.es/cgibin/OnlineJudge?AuthorInfo:29650
http://acm.uva.es/cgibin/OnlineJudge?AuthorInfo:29650

 Experienced poster
 Posts: 105
 Joined: Wed May 25, 2005 7:23 am
Compiler error but works on g++
Here is my perfect g++ code for convex hull 681.
It compiles fine on my cygwin and g++ Wall gives no warnings.
But the judge gives me compile error.Here is the source.
http://rafb.net/paste/results/3Go0wv77.txt
It compiles fine on my cygwin and g++ Wall gives no warnings.
But the judge gives me compile error.Here is the source.
http://rafb.net/paste/results/3Go0wv77.txt

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